The U.S. has been an inefficient energy producer and/or user for the past few decades. With the coming of the "oil crisis" in the 1970's, many modifications were made in order to more efficiently produce energy and utilize our energy resources. Special emphasis was placed on petroleum fuels and the generation of electricity.
While much has been done in the way of conservation with more efficient enggines and better, more efficient generating equipment, the U.S. is still forced to import a substantial portion of its energy needs in the form of petroleum (crude oil). Imported and domestic petroleum, as well as natural gas, are used for out large stationary and mobile combustion installations for electric power generation and production of process heat. This situation is somewhat ironic since in the United States, there if fifteen times as much recoverable coal as recoverable oil and natural gas combined. Coal, therefore, should be the primary fuel for large stationary and mobile combustion installations and for production of process heat. Not only should America's energy needs increasingly by met by coal, but coal could also meet the needs of other industrialized and developing countries. Coal could be America's answer to the balance of trade deficit caused by huge energy imports. However, such is not presently the case.
The greatest deterrent to full utilization, domestic and foreign, of the United States' coal resource is the nature of coal itself. First, raw coal is not a uniform combustion product. Second, as a solid it is difficult to handle and expensive to transport. Third, it contains organic sulfur and nitrogen, which, upon combustion, produce air pollutants which have been associated with acid rain. Fourth, it contains ash which, upon combustion, produces pollutants and slag. In addition to the above problems, the majority of the energy transportation and combustion systems in this country revolve around oil and natural gas which are relatively uniform, pipeline transportable liquid and gaseous fuels. The coal transportation and quality problems are compounded by the fact that, although coal reserves are distributed throughout the United States, coal from different reserves has a wide range of characteristics. Coals, even of the same rank, have different compositions. This limits the interchangeability of coal in combustion systems and thus increases expense and reduces markets. For example, intermountain Western coal, while low in sulfur, is also generally low in BTU per unit weight and has a high water content. Each type of coal requires different pollution control equipment and a specific boiler system. Coal of one region (or even of a particular mine) cannot be efficiently combusted in boilers designed for coal from another source. Therefore, coal is not as uniform a fuel as is, for example, #6 fuel oil.
The inefficient and expensive handling, transportation and storage of the solid material has made the conversion of oil-fired systems to coal less economically attractive. Liquids are much more easily handled, transported, stored and fired into boilers. Because of this nation's dependence on oil and natural gas, existing fuel transportation systems in the U.S., from pipelines to ocean-going tankers, are designed for liquids and gases.
Various methods, for the most part not currently economically viable, have been proposed for converting coal to synthetic liquid or gaseous fuels. Recently developed process technology permits the conversion of coal to synthetic liquid or gaseous fuels at the mine site. While this "synfuel" is more easily transported than coal, the conversion process is capital intensive and requires a great deal of water. The process is also very energy intensive in that a very large portion of the carbon atoms in the coal matrix are converted to hydrocarbons. Despite the high processing costs, the resultant synfuel, like crude oil derived fuels, is valuable as a transportation fuel.
Methods for creating coal slurries or mixtures which facilitate liquid transport and fluidic firing into boiler systems have been proposed but have not been completely successful. To produce a slurry, raw coal is ground, sized, slurried with water or other liquid, and stabilzed. The goal is to obtain a product which handles like a liquid, not only facilitating the transportation step itself, but also reducing labor costs and eliminating the many other handling problems of solids and reducing the capital costs required to convert oil-fired systems to use solid coal.
Previous coal slurries have required special pipelines and pumping equipment. Aqueous coal slurries have additional drawbacks: (1) The water which is necessary to slurry coal is in short supply for coal reserves in the intermountain West. (2) Water must be removed from the slurry and the coal must be dried prior to introduction of the fuel into a furnace or boiler to avoid incurring a substantial heat penalty. (Derating of the boiler) (3) Dewatering and disposal of the slurry water creates a pollution problem.
Liquids other than water, such as alcohol, may be used as the slurrying liquid but are expensive and usually require water for manufacture. In addition to being abrasive, coal slurries tend to settle upon standing, thereby causing flow problems in pipelines and ballast problems aboard ships.
While coal/water slurries and coal/alcohol slurries require substantial system modification in order to be fired in existing oil-fired combustion systems, coal/oil mixtures ("COM") are able to be burned in existing coal-fired furnaces, boilers and process heat generators without substantial equipment modification. COMs, which comprise a pulverized, comminuted or ground coal admixed with oil, may contain various additives to, for example, increase the wetability of the coal, stabilize the mixture, etc. This fuel mixture, while capable of being transmitted by pipeline, requires special handling and pumping equipment. These COMs have received extensive attention in the past decade but they are not new. U.S. Pat. No. 219,181, issued Feb. 24, 1879 to Smith, H. R. and Munsell, H. M. discloses the basic coal/oil mixtures and their use. COMs, while generally having a higher BTU content per unit volume than either coal or oil alone, have serrious draw backs. First, the oil used as the slurry medium draws from the U.S. domestic or foreign supply of crude oil; therefore, it only partially cuts down on this country's foreign oil dependence and reduces our balance of trade deflicit. Second, there are severe restrictions on the export of oil even as a coal/oil mixture, thus there is a limited foreign market. Third, crude oil is expensive and, with the additional slurrying expense, the cost savings to an oil-fired system are marginal. Finally, these COMs have all the inherent drawbacks of coal-containing slurries.
In order to alleviate the above problems of transporting the non-uniform, solid coal energy to the end use facility, an attempt has been made to so-called "co-generate" using electrical generating facilities. There are three main types of co-generating facilities. In all three, the facility is usually place at mine mouth, or in close proximity thereto. In the first, the coal is processed to create synthetic gas or liquid fuel which is fed to a gas turbine that generates electricity. The turbine is exhausted to a heat exchange which produces high temperature process steam. The process steam is utilized for chemical process heat or the like. In a second type, coal is burned directly in a steam boiler to produce steam which drives a turbine. The turbine generates electricity and the exhaust is used as process heat for chemical processes or the like. The third type, the so-called combined cycle cogeneration system, involves the production of synthetic gas from coal which is combusted in a gas turbine to produce electricity. The exhaust gas is heat exchanged to produce steam which drives a second electric generating turbine. The exhaust from this turbine is then used to produce process heat for a chemical plant or the like. Co-generation facilities using the syngas approach have not been altogether successful. This process requires the conversion of all or substantially all of the coal to liquid or gas, which is energy intensive and expensive. Further, as with "synfuels", the product can be a transportation fuel which is easily pipeline transportable and too expensive to be utilized in stationary units. Another disadvantage has been that the electrical facility is limited by the marketability of the process heat generated. Thus, the electric generating facility must operate in conjunction with a chemical plant or some similar process heat user. Additionally, most power generating stations are based upon economies of scale in the 400 to 500 MW range. This has proven expensive in that the capital costs for excess capacity are not justified unless the plant is utilized fully. The size of the plant also limits the sites available for co-generation facilities.
In short, the U.S. energy scene has focused on a number of individual solutions to a many-faceted problem. A fuel "systems" approach is necessary to fully utilize the nation's substantial coal reserves. By forming a modular co-generating system wherein waste heat is used to produce a carbonaceous fuel system which can be readily transported by rail or by pipeline, all of the fuel is utilized efficiently and effectively, yielding flexibility in use and distribution.
Thus it would be highly advantageous to have a co-generating system which would produce electricity while utilizing the process heat in the production of a completely combustible fluidic fuel system which is easily and efficiently prepared from coal using no external water and which would be (a) transportable using existing pipeline, tank car and tankership systems, (b) burnable either directly as a substitute for oil in substantially all existing oil-fired combustion systems with little or no equipment modification or separable at the destination to provide a liquid hydrocarbon fuel or feedstock and a burnable char, (c) a uniform combustion product regardless of the region from which the coal is obtained, (d) high in BTU content per unit volume, (e) low in ash, sulfur and nitrogen, (f) high in solid loading and stability and (g) free of polluting hy-products which would have to be disposed of at the production site or at the destination.